The clinical characteristics of atypical CF are: symptoms that may start in infancy but the disease become clinically significant only after 10 years of age, survival into adulthood, chronic sinopulmonary disease, pancreatic sufficiency, and sweat chloride <60 meq/L. Other patients may present with single organ involvement such as CBAVD, biliary cirrhosis and portal hypertension, chronic or recurrent pancreatitis, giant nasal polyposis or hypochloremic alkalosis. It is recommended to refer such patients for CFTR genotyping, however, absence of known common mutation does not rule out CFTR associated disease, since mutations causing atypical CF are rare and whole genome scan is required for their identification. Nasal PD measurements may be helpful to establish the diagnosis of these patients; however, measurements might be also atypical. Several explanations have been suggested to explain the atypical CF disease.